1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus having the same, which are suitably used in, for example, a video camera, a digital still camera, a monitoring camera, a film camera, and a broadcast camera.
2. Description of the Related Art
A zoom lens for an image pickup apparatus, such as a digital camera or a video camera, is required to include a wide angle area, have a high zoom ratio, and have a back focus of a predetermined length. At the same time, the entire optical system needs to be small. Moreover, the zoom lens is required to have high optical performance over the entire object length from an infinitely distant object to a near object.
It is easy to achieve a high zoom ratio with a positive-lead-type zoom lens, in which a lens unit closest to the object side has positive refracting power. It is easy to reduce the size of the entire optical system with an inner-focus zoom lens, or a rear-focus zoom lens, in which focus is performed by moving the second and subsequent lens units along the optical axis.
U.S. Pat. No. 5,189,557 discloses a zoom lens that includes first to sixth lens units having, in order from the object side to the image side, positive, negative, positive, negative, positive, and negative refracting powers. This zoom lens performs zooming by moving these lens units and performs focusing by moving the sixth lens unit.
Japanese Patent Laid-Open No. 2004-317867 discloses a rear-focusing zoom lens including seven lens units having, in order from the object side to the image side, positive, negative, positive, negative, positive, negative, and positive refracting powers. This zoom lens performs zooming by moving six lens units on the object side and performs focusing with the sixth lens unit.
In general, a small zoom lens having a predetermined zoom ratio may be realized by increasing the refracting powers (i.e., the optical power: the reciprocal of the focal length) of the lens units constituting the zoom lens while reducing the number of the lenses. However, this increases variation of aberrations associated with zooming and focusing, making it difficult to achieve high optical performance over the entire zoom range and object length.
In order to achieve a positive-lead type zoom lens having high optical performance over the entire zoom range and object length, the zoom type, the powers of the lens units, and the lens configurations of the lens units need to be appropriately set.
The present invention provides a small zoom lens having a wide angle of view, a high zoom ratio, and high optical performance over the entire zoom range, and an image pickup apparatus having such a zoom lens.